--- a/browser/locales/Makefile.in
+++ b/browser/locales/Makefile.in
@@ -31,20 +31,20 @@ MOZ_PKG_MAC_DSSTORE=$(ABS_DIST)/branding
 MOZ_PKG_MAC_BACKGROUND=$(ABS_DIST)/branding/background.png
 MOZ_PKG_MAC_ICON=$(ABS_DIST)/branding/disk.icns
 MOZ_PKG_MAC_EXTRA=--symlink '/Applications:/ '
 endif
 
 MOZ_SFX_PACKAGE=$(topsrcdir)/other-licenses/7zstub/firefox/7zSD.sfx
 MOZ_INSTALLER_PATH=$(topsrcdir)/browser/installer/windows
 
-SEARCHPLUGINS_FILENAMES := $(shell $(call py_action,output_searchplugins_list,$(srcdir)/search/list.json $(AB_CD)))
+SEARCHPLUGINS_FILENAMES := $(or $(shell $(call py_action,output_searchplugins_list,$(srcdir)/search/list.json $(AB_CD))), $(error Missing search plugins))
 SEARCHPLUGINS_PATH := .deps/generated_$(AB_CD)
 SEARCHPLUGINS_TARGET := libs searchplugins
-SEARCHPLUGINS := $(foreach plugin,$(addsuffix .xml,$(SEARCHPLUGINS_FILENAMES)),$(or $(wildcard $(srcdir)/searchplugins/$(plugin)),$(warning Missing searchplugin: $(plugin))))
+SEARCHPLUGINS := $(foreach plugin,$(addsuffix .xml,$(SEARCHPLUGINS_FILENAMES)),$(or $(wildcard $(srcdir)/searchplugins/$(plugin)),$(error Missing searchplugin: $(plugin))))
 # Some locale-specific search plugins may have preprocessor directives, but the
 # default en-US ones do not.
 SEARCHPLUGINS_FLAGS := --silence-missing-directive-warnings
 PP_TARGETS += SEARCHPLUGINS
 
 list-json = $(SEARCHPLUGINS_PATH)/list.json
 GARBAGE += $(list-json)